Non-metallic Charge Carriers in Aqueous Batteries


Student thesis: Doctoral Thesis

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Awarding Institution
Award date4 Jun 2020


Charge carrier is one fundamental component in battery configurations, which could directly determine battery output performance. While metallic charge carriers (MCC) are conventionally employed in aqueous battery systems, the non-metallic charge carriers (NMCC) have recently verified to endow aqueous batteries with outstanding performance characteristics, such as ultra-fast kinetics, super-durable cyclic lifetime, flat working voltage plateau and low-cost. NMCC could not only insert throughout electrode framework and form covalent-ionic bonds with host electrode framework, but also serve as reversible redox centers for electrode reactions, resulting in superior performance. 

At every beginning, all species of cationic and anionic NMCC are summarized, investigating their charge storage mechanisms and ion interacting manners throughout electrode. The physicochemical properties, prerequisites and existing challenges of adopting NMCC are discussed to figure out their electrochemical nature and interior relationships with battery output performance. Lastly, the designing principle of NMCC based batteries are elaborated, mainly upon selection criteria of electrode materials with well-designed electrode reactions to realize aqueous NMCC-based batteries with high-performance.

Subsequently, we have developed different NMCC species to embody the functionalities of NMCC in four battery systems. Firstly, building aqueous acidic batteries is in its infancy. There have been several sporadic attempts that showed desirable electrochemical performance, especially rate stability and high-power density. The direct use of metal anode is regarded as the best protocol for fabricating metal-based batteries. However, introducing acid-tolerant and electrochemically reversible metal anode into an acidic aqueous battery system remains a considerable challenge. In this work, we used copper (Cu) metal as a reversible metal anode to match acidic regimes with a nearly 100% deposition-dissolution efficiency. The reaction kinetics and mechanism of the Cu anode can be regulated by protons with 400% kinetic acceleration compared with the mild electrolyte. In addition, the anode exhibited dendrite-free morphology after cycling due to the surface roughening effect, which is different from the morphologies of widely used Zn and Li metal anodes. When coupled with Prussian blue analogue as cathodes to host Cu2+ and H+-ions, the battery delivered ultra-fast kinetics of 1830 W kg-1 at 75 C, which is comparable to the power performance of supercapacitors. Long-term cyclic stability was evaluated, where the capacity retention was 85.6% after 5000 cycles. Finally, flexible fiber-shaped acidic Cu-based batteries are demonstrated for potential wearable applications.

Another non-metallic ammonium (NH4+) ions are applied as charge carriers for aqueous batteries, where hexagonal MoO3 was initially investigated as an anode candidate for NH4+ storage. From experimental and first-principle calculated results, the battery chemistry proceeds with reversible building-breaking behaviors of hydrogen bonds between NH4+ and tunneled MoO3 electrode frameworks, where the ammoniation/de-ammoniation mechanism is dominated by non-diffusion-controlled pseudocapacitive behavior. Outstanding electrochemical performance of MoO3 for NH4+ storage was delivered with 115 mAh g-1 at 1 C and could retain 32 mAh g-1 at 150 C. Furthermore, it remarkably exhibited ultra-long and stable cyclic performance up to 100,000 cycle with 94% capacity retention and high power density of 4170 W kg-1 at 150 C. When coupled with CuFe PBA cathode, the full ammonium battery could deliver decent energy density 21.3 Wh kg-1 and the resultant flexible ammonium batteries at device level were also pioneeringly developed for potential realistic applications.

Alkaline Silver (Ag)-Znic (Zn) batteries have been suffering from poor cyclic stability for over one century but the comprehensively improving protocol is still in vacancy with big challenge. Here, we commence a mild Ag-Zn battery to simultaneously solve the cathode dissolving issue and anode dendrite issue by adopting Cl- ions. The battery proceeds through anionic halides as charging carriers for cathode reactions, endowing two phase transition process with ultra-flat discharging voltage plateau. The battery delivered unprecedently elongated cyclic lifetime to 1300 cycles in contrast to conventional alkaline Ag-Zn battery (<100 cycles). This work not only solved the long-term cyclic issue of Ag-Zn battery but also would act as a model system to introduce mild electrolyte and anionic charging carriers into other aqueous battery systems for performance improvement. 

In summary, the electrochemical nature of NMCC based batteries are investigated, including protons, i.e., H+-ions, ammonium ions (NH4+) and chloride ions (Cl-). Special attentions have been adopted to various aspects from reaction mechanisms, electrode materials and electrolyte, which targeted at figuring out the design principle and selection criteria of battery reactions and materials. In addition, the as-obtained batteries are situated in realistic applications in wearable electronics and large-scale storage, which was derived from two outstanding advantages of aqueous batteries as intrinsic safety and low-cost.

    Research areas

  • Aqueous battery chemistry, Non-metallic charge carriers, Copper-based battery, Ammonium-ion battery, Chloride-ion battery